This invention relates to coated granular fertilizers and a method for producing same. More particularly, this invention relates to granular fertilizers coated with a resin coating layer in which fine powder is uniformly distributed and by which influence of temperature upon the dissolution-out of fertilizer component is controlled and also relates to a method for producing same.
Concomitant with modernization of agriculture, there has been arising a demand of fertilizer having various functions. Among them coated granular fertilizers, as a type of fertilizer capable of controlling dissolution-out of fertilizer component so as to be able to feed nutritious matter required by plants over the entire range of its growing period only by one time application of fertilizer have been drawing general attention. As fertilizers of this kind, those coated with sulfur, wax, and resins have become commercialized. We developed a method for controlling freely the dissolution-out rate of fertilizer by completely coating with a polyolefin and controlling the moisture permeability of the coating and disclosed it in U.S. Pat. No. 4,019,890. The dissolution-out of component from these fertilizers, particularly from those coated with a resin shows preset effectiveness as fertilizer without receiving the influence of field condition e.g. kind of soil, water content, pH, and microorganisms but on the other hand, it is liable to receive a great deal of influence of temperature. This property accords with absorption of nutritious matters by plants and in this regard, is preferable in some cases but in most of the cases, it is preferable to weaken such an influence. Thus, the advent of fertilizers which show much less tendency of receiving influence of temperature in the dissolution-out of fertilizer component has been desired.
Accordingly, it is an object of the present invention to provide a fertilizer coated with a coating layer having a controlled moisture permeability and a controlled temperature dependency of the moisture permeability.
It is another object of the present invention to provide a method for producing such a fertilizer.